The invention relates to a process and apparatus for the thermal measurement of mass flow.
In prior art processes the mass flow is passed through a hollow body and its inlet and outlet temperature are measured. In a particular process of this type a flowing fluid is heated by a predetermined amount of heating power and the temperature rise of the fluid is then measured (Laub, J. H. "Read massflow directly with thermal flowmeters", Cont. Eng., April 1966, S. 69-72).
An apparatus operating by this principle is the so-called "Thomas-meter". It comprises a tube with an interior heating coil which includes resistance thermometers ahead of and behind the heating coil. The heating power is kept at a constant level and the temperature difference appearing at the resistance thermometers is then determined.
This prior art apparatus, however, requires that the heat supplied is fully transmitted to the fluid. This is possible only in case of materials with a high heat transfer number. The Thomas-meter and similar apparatus are therefore adapted mainly for measurements of fluids, while in case of media with a low heat transfer number they do not give correct results because of the unrecorded heat losses such as radiation loss and heat loss occurring through the tube wall.
There is also known a coloric meter for steam or heat amounts (West German Pat. No. 590,825) wherein the flowing medium must release all of its heat contents to a cooling agent and wherein the heat flow passing through the wall of the heat exchanger is determined by means of a multiplicity of in series arranged thermocouples. This prior art apparatus, however, is rather complex and costly.
It is therefore an object of the invention to provide for a process and simplified apparatus of the general type indicated which permits the exact measurement also in case of media which have a low heat transfer number.